Extragalactic planet

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An extragalactic planet, also known as an extragalactic exoplanet or an extroplanet, [1] [2] [3] is a star-bound planet or rogue planet located outside of the Milky Way Galaxy. Due to the immense distances to such worlds, they would be very hard to detect directly. However, indirect evidences suggest that such planets exist. [4] [5] [6] [7] [8] Nonetheless, the most distant individually confirmed planets are SWEEPS-11 and SWEEPS-04, located in Sagittarius, approximately 27,710 light-years from the Sun, while the Milky Way is about 87,400 light-years in diameter. This means that even galactic planets located further than that distance have not been individually confirmed.

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Confirmed extragalactic planets

Confirmed from gravitational microlensing

A population of unbound planets between stars, with masses ranging from Lunar to Jovian masses, was indirectly detected, for the first time, by astrophysicists from the University of Oklahoma in 2018, in the lensing galaxy that lenses quasar RX J1131-1231 by microlensing. [4] [5] [6] Later, two other similar populations were detected in the galaxies of the galaxy-quasar lensing systems Q J0158-4325 and SDSS J1004+4112, whose foreground members are 3.6 billion and 6.3 billion light-years away, respectively. These objects also could be a mix of low-mass rogue planets and primordial black holes. [7] [8]

Candidate extragalactic planets

Candidates from gravitational microlensing

A microlensing event in the Twin Quasar gravitational lensing system was observed in 1996, by R. E. Schild, in the "A" lobe of the lensed quasar. It is predicted that a 3-Earth-mass planet in the lensing galaxy, YGKOW G1, caused the event. This was the first extragalactic planet candidate announced. This, however, is not a repeatable observation, as it was a one-time chance alignment. This predicted planet lies 4 billion light years away. [9] [10]

PA-99-N2 b

A team of scientists has used gravitational microlensing to come up with a tentative detection of an extragalactic exoplanet in Andromeda, the Milky Way's nearest large galactic neighbor. The lensing pattern fits a star with a smaller companion, PA-99-N2, weighing just around 6.34 times the mass of Jupiter. This suspected planet is the first announced in the Andromeda Galaxy. [11] [12]

Candidates around extragalactic black-holes and X-ray binaries

IGR J12580+0134

In 2016, a tidal disruption event was detected on the 9,150,000 M☉ supermassive black hole IGR J12580+0134, which was caused by the destruction of a 8–40  MJ object by the black hole. IGR J12580+0134 is 17 million parsecs (55 million light-years) away from Earth. [13]

M51-ULS-1b

In September 2020, the detection of a candidate planet orbiting the high-mass X-ray binary M51-ULS-1 in the Whirlpool Galaxy was announced. The planet was detected by eclipses of the X-ray source, [1] which consists of a stellar remnant (either a neutron star or a black hole [2] ) and a massive star, likely a B-type supergiant. The planet is 0.7 RJ or around 50,000 kilometers in radius. [14] and orbit at a distance of some tens of AU. [15] [16] The study of M51-ULS-1b as the first known extragalactic planet candidate was published in Nature in October 2021. [17]

Candidates around formerly extragalactic stars

Disrupted planets of runaway stars

The subdwarf star HD 134440, which is currently located in galactic halo and has extragalactic origin, was found to have a significantly higher metallicity than the similar star HD 134439. In 2018, this was believed to resulted from an engulfment of orbiting planets by HD 134440. [18]

BD+20 2457 b and BD+20 2457 c

The bright giant star BD+20 2457 was proposed to host two super-Jupiter planets or brown dwarfs, although the claimed planetary system is not dynamically stable. [19] As BD+20 2457 is a halo star possibly having formed in the Gaia Enceladus, which are galactic remains of a former galaxy, the star and its planets might be extragalactic in origin. [20]

Refuted extragalactic planets

HIP 13044 b

A planet with a mass of at least 1.25 times that of Jupiter had been potentially discovered by the European Southern Observatory (ESO) orbiting a star of extragalactic origin, even though the star currently has been absorbed by our own galaxy. HIP 13044 is a star about 2,000 light years away in the southern constellation of Fornax, [21] part of the Helmi stream of stars, a leftover remnant of a small galaxy that collided with and was absorbed by the Milky Way over 6 billion years ago. [22]

However, subsequent analysis of the data revealed problems with the potential planetary detection: for example an erroneous barycentric correction had been applied (the same error had also led to claims of planets around HIP 11952 that were subsequently refuted). After applying the corrections, there is no evidence for a planet orbiting the star. [23] If it had been real, the Jupiter-like planet would have been particularly interesting, orbiting a star nearing the end of its life and seemingly about to be engulfed by it, potentially providing an observational model for the fate of our own planetary system in the distant future (cf. Future of Earth).

See also

Related Research Articles

<span class="mw-page-title-main">Exoplanet</span> Planet outside the Solar System

An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not then recognized as such. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detected in 1988, was confirmed in 2003. As of 19 December 2024, there are 5,811 confirmed exoplanets in 4,340 planetary systems, with 973 systems having more than one planet. In collaboration with ground-based and other space-based observatories the James Webb Space Telescope (JWST) is expected to give more insight into exoplanet traits, such as their composition, environmental conditions, and potential for life.

<span class="mw-page-title-main">Rogue planet</span> Planets not gravitationally bound to a star

A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf.

<span class="mw-page-title-main">Gravitational microlensing</span> Astronomical phenomenon due to the gravitational lens effect

Gravitational microlensing is an astronomical phenomenon caused by the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light. These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light.

<span class="mw-page-title-main">Exomoon</span> Moon beyond the Solar System

An exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body.

<span class="mw-page-title-main">Optical Gravitational Lensing Experiment</span> Long-term variability sky survey

The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detection and classification of variable stars, discovery of microlensing events, dwarf novae, and studies of the structure of the Galaxy and the Magellanic Clouds. Since the project began in 1992, it has discovered a multitude of extrasolar planets, together with the first planet discovered using the transit method (OGLE-TR-56b) and gravitational microlensing. The project has been led by professor Andrzej Udalski since its inception.

<span class="mw-page-title-main">Methods of detecting exoplanets</span>

Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the exoplanets reported as of January 2024 have been observed directly, with even fewer being resolved from their host star.

<span class="mw-page-title-main">Super-Earth</span> Type of exoplanet

A Super-Earth or super-terran or super-tellurian is a type of exoplanet with a mass higher than Earth, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17.1 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.

OGLE-2005-BLG-071L is a distant, magnitude 19.5 galactic bulge star located in the constellation Scorpius, approximately 11,000 light years away from the Solar System. The star is probably a red dwarf with a mass 43% of that of the Sun.

<span class="mw-page-title-main">Circumbinary planet</span> Planet that orbits two stars instead of one

A circumbinary planet is a planet that orbits two stars instead of one. The two stars orbit each other in a binary system, while the planet typically orbits farther from the center of the system than either of the two stars. In contrast, circumstellar planets in a binary system have stable orbits around one of the two stars, closer in than the orbital distance of the other star. Studies in 2013 showed that there is a strong hint that a circumbinary planet and its stars originate from a single disk.

<span class="mw-page-title-main">BD+20 2457</span> Bright giant star in the constellation Leo

BD+20 2457 is a 10th-magnitude K-type bright giant star located approximately 4,800 light-years away in the constellation of Leo. The name refers to the Bonner Durchmusterung star catalog. This star contains a very small amount of metals, containing only 10% as enriched with elements heavier than hydrogen and helium as the Sun.

<span class="mw-page-title-main">Discoveries of exoplanets</span> Detecting planets located outside the Solar System

An exoplanet is a planet located outside the Solar System. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such until 2016; no planet discovery has yet come from that evidence. What turned out to be the first detection of an exoplanet was published among a list of possible candidates in 1988, though not confirmed until 2003. The first confirmed detection came in 1992, with the discovery of terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method and the radial-velocity method. As of 24 July 2024, there are 7,026 confirmed exoplanets in 4,949 planetary systems, with 1007 systems having more than one planet. This is a list of the most notable discoveries.

A blanet is a member of a hypothetical class of exoplanets that directly orbit black holes.

References

  1. 1 2 Smith, Kiona (26 October 2021). "Extroplanet: Astronomers may have just found the first planet outside our galaxy". Inverse. Retrieved 2021-11-08.
  2. 1 2 Planet Song M51 ULS 1b Messier 51 Whirlpool Galaxy, 6 November 2021, retrieved 2021-11-08
  3. ↑ Sandhya Ramesh (2021-10-29). "NASA telescope may have just helped find the first planet spotted outside Milky Way". ThePrint. Retrieved 2021-11-08.
  4. 1 2 Dai, Xinyu; Guerras, Eduardo (2 February 2018). "Probing Planets in Extragalactic Galaxies Using Quasar Microlensing". The Astrophysical Journal. 853 (2): L27. arXiv: 1802.00049 . Bibcode:2018ApJ...853L..27D. doi: 10.3847/2041-8213/aaa5fb . S2CID   119078402.
  5. 1 2 Zachos, Elaine (5 February 2018). "More Than a Trillion Planets Could Exist Beyond Our Galaxy - A new study gives the first evidence that exoplanets exist beyond the Milky Way". National Geographic Society . Archived from the original on February 5, 2018. Retrieved 5 February 2018.
  6. 1 2 Mandelbaum, Ryan F. (5 February 2018). "Scientists Find Evidence of Thousands of Planets in Distant Galaxy". Gizmodo . Retrieved 5 February 2018.
  7. 1 2 Bhatiani, Saloni; Dai, Xinyu; Guerras, Eduardo (November 2019). "Confirmation of Planet-mass Objects in Extragalactic Systems". The Astrophysical Journal. 885 (1): 77. arXiv: 1909.11610 . Bibcode:2019ApJ...885...77B. doi: 10.3847/1538-4357/ab46ac . ISSN   0004-637X.
  8. 1 2 Lazaro, Enrico de (November 2019). "Free-Floating Planet-Mass Objects are Common in Galaxies | Sci.News". Sci.News: Breaking Science News. Retrieved 2024-11-17.
  9. ↑ Schilling, Govert (6 July 1996). "Do alien worlds throng faraway galaxy?". New Scientist. No. 2037.
  10. ↑ Extrasolar Visions, "The Q0957+561 Planet" Archived 2012-03-30 at the Wayback Machine (accessed 1 September 2009)
  11. ↑ "First extragalactic exoplanet may have been found by gravitational microlensing". Thaindian News. 11 June 2009. Archived from the original on 2009-06-24.
  12. ↑ Battersby, Stephen (10 June 2009). "First extragalactic exoplanet may have been found". New Scientist.
  13. ↑ Lei, Wei-Hua; Yuan, Qiang; Zhang, Bing; Wang, Daniel (December 2015). "Igr J12580+0134: The First Tidal Disruption Event with an Off-Beam Relativistic Jet". The Astrophysical Journal. 816 (1): 20. arXiv: 1511.01206 . doi: 10.3847/0004-637X/816/1/20 . ISSN   0004-637X.
  14. ↑ "Planet M51-ULS-1 B". 2020.
  15. ↑ Di Stefano, R.; et al. (18 September 2020). "M51-ULS-1b: The First Candidate for a Planet in an External Galaxy". arXiv: 2009.08987 [astro-ph.HE].
  16. ↑ Crane, Leah (23 September 2020). "Astronomers may have found the first planet in another galaxy". New Scientist . Retrieved 25 September 2020.
  17. ↑ Di Stefano, Rosanne; Berndtsson, Julia; Urquhart, Ryan; Soria, Roberto; Kashyap, Vinay L.; Carmichael, Theron W.; Imara, Nia (2021-10-25). "A possible planet candidate in an external galaxy detected through X-ray transit". Nature Astronomy. 5 (12): 1297–1307. arXiv: 2009.08987 . Bibcode:2021NatAs...5.1297D. doi:10.1038/s41550-021-01495-w. ISSN   2397-3366. S2CID   256726097.
  18. ↑ Reggiani, Henrique; Meléndez, Jorge (December 1, 2018). "Evidences of extragalactic origin and planet engulfment in the metal-poor twin pair HD 134439/HD 134440". Monthly Notices of the Royal Astronomical Society. 475 (3): 3502–3510. arXiv: 1802.07469 . Bibcode:2018MNRAS.475.3502R. doi: 10.1093/mnras/sty104 . ISSN   0035-8711 . Retrieved 10 May 2018.
  19. ↑ Horner, J.; Wittenmyer, R. A.; Hinse, T. C.; Marshall, J. P. (2014). "A dynamical investigation of the proposed BD +20 2457 system". Monthly Notices of the Royal Astronomical Society. 439 (1): 1176–1181. arXiv: 1401.2793 . Bibcode:2014MNRAS.439.1176H. doi: 10.1093/mnras/stu081 . S2CID   54534748.
  20. ↑ Perottoni, Hélio D.; Amarante, João A. S.; Limberg, Guilherme; Rocha-Pinto, Helio J.; Rossi, Silvia; Anders, Friedrich; Borbolato, Lais (May 2021). "Searching for Extragalactic Exoplanetary Systems: The Curious Case of BD+20 2457". The Astrophysical Journal. 913 (1): L3. arXiv: 2104.08306 . Bibcode:2021ApJ...913L...3P. doi: 10.3847/2041-8213/abfb06 . ISSN   0004-637X.
  21. ↑ "Planet from another galaxy discovered". ESO Press Release. 18 November 2010. Retrieved 17 November 2011.
  22. ↑ Klement, R.; Setiawan, J.; Thomas Henning; Hans-Walter Rix; Boyke Rochau; Jens Rodmann; Tim Schulze-Hartung; MPIA Heidelberg; ESTEC (2011). "The visitor from an ancient galaxy: A planetary companion around an old, metal-poor red horizontal branch star". The Astrophysics of Planetary Systems: Formation, Structure, and Dynamical Evolution. IAU Symposium. Vol. 276. Proceedings of the International Astronomical Union. pp. 121–125. arXiv: 1011.4938 . Bibcode:2011IAUS..276..121K. doi:10.1017/S1743921311020059.
  23. ↑ Jones, M. I.; Jenkins, J. S. (2014). "No evidence of the planet orbiting the extremely metal-poor extragalactic star HIP 13044". Astronomy & Astrophysics. 562: id.A129. arXiv: 1401.0517 . Bibcode:2014A&A...562A.129J. doi:10.1051/0004-6361/201322132. S2CID   55365608.
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